Transverse, axial and torsional strain in ReBCO tapes; experiments - - PowerPoint PPT Presentation

Transverse, axial and torsional strain in ReBCO tapes; experiments and models

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• C. Zhou1, K. Ilin1, K. A. Yagotintsev1, P. Gao1, J. Kosse1, M. Dhalle1, W. A. J. Wessel1, H. J. G. Krooshoop1, T. J.

Haugan2, D. C. van der Laan3, A. Nijhuis1

• 1. University of Twente, Faculty of Science & Technology, The Netherlands
• 2. US Air Force Research Laboratory, USA
• 3. Advanced Conductor Technologies and University of Colorado, USA

ICEC/ICMC 2014 Enschede, the Netherlands

Outline

• Introduction
• Experimental setups

 ReBCO tape torsion-tensile studies  Transverse stress on ReBCO tapes

• Results and analysis
• Summary

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• Introduction. ReBCO cabling methods
• Conductor on Round Core (CORC)
• Twisted Stack-Tape Cable
• Roebel Cable

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D.C. van der Laan, SUST 22, 065013 (2009).

Tape performance when subjected to (combined) torsion, tensile and transverse loading is the key to understand limitations for cable performance.

• M. Takayasu, IEEE 23, 4800104 (2013).
• W. Goldacker, Journal of Physics, 43 (2006).

After test: damaged tapes in outer layers due to cable bending

Objective

Modeling of the stress-strain state in a REBCO tape at various loads (temperature, tensile, torsion, transverse load, etc.) Tensile Torsion Transverse The ultimate goal is to predict the critical strain level of the tape under cabled conditions Plot of normalized critical current vs. applied axial stress on a 4 mm wide, SCS4050 SuperPower 2G HTS wire

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ABAQUS software for modelling with mechanical material properties as inputs (from litt & dedicated experiments)

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ReBCO torsion – tensile test

L-tape=175 mm 5 Vtap pairs Torsional angles used in combiend torsion-tensile tests: 00 - 𝜁𝑢𝑝𝑠~0% 3000 - 𝜁𝑢𝑝𝑠~0.31 % 4800 - 𝜁𝑢𝑝𝑠~0.5 % Torsion under controlled axial tensile load by linear stage from TARSIS facility. Sample - SuperPower SCS 4050 tape

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Tape transverse stress setup

Transverse stress at 77 K, calibrated strain gauge for applied force measurement. Different types of pushing heads allow to control pushing area and stress. sample

Modeling Assumptions (ABAQUS)

• Degradation of the critical current depending
• n the strain state of the REBCO layer at the

instant of crack initiation (K. Osamura et al.)

• Buffer layers and silver layers do not

significantly influence the mechanical behavior

• f the tape

Configuration of SuperPower 2G HTS Tape SCS4050

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State of residual strain on the REBCO layer as a function of applied external tensile strain at RT. (Kozo Osamura et al.)

Crack initiation Applied external strain, % REBCO strain, %

0.45 0.7

• SCS4050 SuperPower tape for most

experiments and modeling Tensile Torsion Transverse

Modeling: properties of materials

Tape SCS4050:

• Substrate

(Hastelloy C-276)

• Copper

(Electroplating)

• REBCO

It is necessary to model the production process because of the thermal residual strain (~ -0.2 %) at RT in the REBCO layer. Needed: thermal expansion coefficients and elasto-plastic material properties depending on temperature.

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Simulation results: tensile

Tape (RT) Tape (77K) Cu (RT) Cu (77K) Hasttelloy (RT) Hasttelloy (77K)

FEM (RT) FEM (77K)

Tensile test and FEM stress vs. strain data for the tape SCS4050 at RT and 77K.

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Crack initiation FEM Applied external strain, % REBCO strain, % 0.45 0.7

State of residual strain on the REBCO layer as a function of applied external tensile strain at RT from neutron diffraction experiment (Kozo Osamura et al.) and FEM results at RT.

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FEM Experiment Reversibility region Permanent degradation region

Results: torsion - tensile

Critical strain in REBCO layer as a function of applied external tensile strain and applied torsion strain at 77K

Applied twist pitch, grad/mm

FEM simulation: Tensile – Torsion at 77 K. Longitudinal strain in REBCO layer

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Transverse stress on SuperPower SCS4050

4mm pushing head 1mm pushing head

• Tape thickness not uniform over tape width.
• Non homogenous pressure distribution causes early degradation

0.089mm 0.094mm 0.084mm

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Critical transverse pressure as a function of copper layer thickness at 77K

FEM results: transverse load, thickness of the copper

REBCO strain Contact Pressure

Longitudinal strain in ReBCO layer

40 um Cu 100 um Cu

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Transverse stress micrographs and SEM

Summary

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• Systematic studies of ReBCO tapes under twist, tensile and transverse load were

performed.

• SCS4050 tape shows good Ic reversibility for tensile axial strain up to 𝜁 =0.55%. For

combined torsion–tensile loading, increase in torsion strain leads to earlier and more gradual Ic degradation upon a controlled applied tensile axial strain.

• Locally transverse applied stress leads to crack formation mostly at the edges of the

pushing area. SEM analysis and modeling are in good agreement for peak in plane strain concentrations.

• The homogeneity of applied stress plays a significant role just as the thickness of the

tape layers (copper) causing stress concentration spots.